1. Field of the Invention
The present invention relates to a control technique for a data storage system comprising two or more separately established host devices.
Furthermore, the present invention relates to an exclusive control technique for duplicated volumes generated between two separately established storage devices having a remote copy function.
2. Description of the Related Art
The various IT technologies for sustaining 24-hour service without a system stoppage are of particular interest to companies promoting e-business development. One of those is clustering, a technology for realizing high availability. This technology is used mainly for systems performing database operations, wherein systems of multiple devices are combined and constructed so that the entire system can work without stopping even when part of the system fails. For example, a small scale system has a constitution using a single shared disk among a plurality of servers and a SCSI interface is used between the servers and the shared disk. If data handled by the plurality of servers is placed on the shared disk in this constitution, another server takes over the data on the shared disk and can continue processing if one server goes down. This is called a fail-over. In a clustering system carrying out a fail-over in this way, operations are carried out so that a client can continue to use a single server.
In order for uniform determination of the host devices for performing fail-over in the clustering system, MSCS (Microsoft cluster server), a clustering product from Microsoft, has a single determining volume, called a quorum resource, for controlling the cluster configuration information.
There is exclusive control of this determining volume and this avoids the problem losing data integrity because of redundant possible error in source processing of a plurality of different processes at the same time on a single resource.
Next is explained a clustering system in the case of two or more host devices and two storage devices connected by a SCSI interface. In the clustering system, the host devices are each connected with a network interface. The host devices monitor each other's operating status by sending messages to each other and performing heartbeat communications.
Furthermore, the clustering system detects when a failure occurs in a host device or in the network interface and heartbeat communications become impossible, and determines whether to continue with resources, applications, and services on another host device. A single determining volume for managing the clustering system is established in the storage devices as the sole element for making that determination.
Generally, in systems using a SCSI interface, one of a plurality of hosts has exclusive control (exclusive use) of a single target (for example, a magnetic disk drive). In such cases, it is possible to reserve a target and have the exclusive use thereof by initially issuing a SCSI reserve command.
In the case where a failure occurs in the host device or in the network interface and heartbeat communications become impossible, each of the host devices, in order to acquire exclusive usage rights in the clustering system, issues a SCSI reserve command to the determining volume and attempts to acquire exclusive usage rights. The host device whose SCSI reserve command to the determining volume was successful takes over all applications and services of other host devices and resources such as disk volumes and executes a fail-over. Meanwhile, the host devices whose SCSI reserve commands to the determining volume failed halt applications and services being performed thereon.
In this way, the clustering system realizes a state where one host device has exclusive use of the determining volume for managing the clustering system.